Field of the Invention
The invention relates to a non-volatile semiconductor memory device, especially relates to a storage device having NAND type string and an erasing method thereof.
Description of Related Art
Flash memory is a memory element that is applied to a wide variety of electronic equipments, such as digital camera, smartphone, etc. In the market, the flash memory is further required to be small in volume and large in capacity, and is further required to have high speed and low power consumption.
The NAND type flash memory has a memory array configured to have a plurality of blocks, the block is formed by configuring a plurality of NAND strings in column direction. The NAND string is formed by a plurality of memory cells connected in series and select transistors connected to two ends of the series, wherein one end is connected to the bit line via a bit line side select transistor, and another end is connected to the source line via a source line side select transistor.
In the NAND type flash memory, data erasing is executed in block units. At this point, the word line of the selected block is set as 0V or lower than P-well voltage, a long positive voltage erase pulse is applied to the P-well forming the memory cell array, and after the erase pulse is applied, the electric potential of the P-well is restored to 0V. After erasing, by verifying read-out, the threshold value of the memory cell inside the selected block is determined whether to be smaller than a specific value. If the threshold value of all of the cell units inside the block is smaller than the specific value, the erase operation is completed, but if the threshold value of a part of the cell units is higher than the specific value, the erase pulse PS is applied again and the verifying read-out is executed again (such as Japan patent publication 2012-027979).
In the future, along with the popularity of internet devices, power consumption of the electronic equipment is restricted, and high-speed data communication between electronic equipments is desired. Consequently, the flash memory powered by the electronic equipment is also further required to have low power consumption.